“Biochip” is the generic term for devices in which probe biomolecules that react with to-be-detected target biomolecules in a specific manner are fixed at predetermined positions on a chip surface. A deoxyribonucleic acid (DNA) chip that is atypical example of the biochip is used to detect the types and amounts of target DNA included in blood or cell extract. The DNA chip has, for example, a structure in which thousands to tens of thousands of types of probe DNA, each being single-chain DNA having a known sequence, are arranged in an array on a substrate such as a glass slide.
When a to-be-examined liquid containing fluorescence-marked target DNA is supplied to the DNA chip, only the target DNA which has sequences complementary to the sequences of the probe DNA is bonded to the probe DNA by hydrogen-bonding to form a complementary double chain. As a result, the parts to which the target DNA is fixed is fluorescent-colored. By measuring the position and coloring intensity of the fluorescent-colored parts on the chip, the types and amounts of the target DNA can be detected. Therefore, as described in a published Japanese translations of PCT international publication for patent applications 2002-537869, when the DNA chip is manufactured, the probe DNA having a predetermined sequence should be fixed only on a predetermined portion on a surface of the substrate. However, it is difficult to fix the probe DNA only in the specific location. Therefore, the target DNA bonded to the probe DNA fixed in location other than the specific location becomes background noise in a detection process. It becomes a factor to decrease a detection accuracy of the DNA chip.